Stack injection molding apparatus with separately actuated arrays of valve gates

ABSTRACT

A stack injection molding apparatus has first and second arrays of valve gate injection nozzles and separate mechanisms for independently actuating the nozzles of each array. A separate reciprocating yoke plate engages the valve pins of each nozzle array, and is actuated by either one centrally located actuator or a pair of symmetrically located actuators.

[0001] This invention relates generally to stack injection molding and,more particularly, to a stack molding system having a plurality of valvegates commonly actuated by a uniform motion transferring mechanism.

BACKGROUND OF THE INVENTION

[0002] In multi-cavity stack injection molding systems, accurate controlof resin melt flow from a hot runner manifold to all of the moldcavities is essential to achieving uniformity of the molded articles.The reciprocating valve pins used to control the gates to the cavitiestypically are operated simultaneously, which requires even loading ofthe valve pins. Compactness and simplicity of the machinery also areimportant considerations from the standpoint of cost, reliability andefficient heat transfer.

[0003] Representative examples of known stack injection molding systemsare disclosed in U.S. Pat. Nos. 4,212,627; 4,244,909; 4,891,001;5,013,235; 5,460,510; 5,478,230; and 5,533,882. Some of these employ aseparate actuator for each valve pin, or a separate actuator for eachopposed pair of valve pins. U.S. Pat. No. 4,212,627 discloses a stackmolding arrangement wherein a single hydraulic actuator simultaneouslymoves all of the valve pins of two arrays of injection nozzles through acomplex multi-link slide bar mechanism. This arrangement ensuressimultaneous valve pin movement, but it tends to require frequentmaintenance and does not permit any flexibility in operation, such asdifferential opening or closing of the two arrays of injection nozzles.

[0004] In single-face molding machines various arrangements are knownfor simultaneously actuating a single array of valve pins. See, forexample, U.S. Pat. No. 4,095,931 (sliding cam rod); U.S. Pat. No.4,330,258 and WO 00/43187 (rack and pinion drive); and JP 9141688(reciprocating plate). Other valve pin actuating mechanisms aredisclosed in U.S. Pat. No. 4,378,963; U.S. Pat. No. 4,669,971; U.S. Pat.No. 4,712,995; U.S. Pat. No. 4,917,594; U.S. Pat. No. 4,923,387; U.S.Pat. No. 5,368,470; DE 3733363; DE 4230758; and DE 4231270. However, thetechnology used in such arrangements has not been of much benefit tostack molding apparatus, which generally tend to be complex, cumbersome,expensive, subject to premature wear, and/or unreliable. A need exists,therefore, for an improved stack molding apparatus that is durable andcompact, allows for flexibility of operation, and efficiently andreliably produces molded products of good quality.

SUMMARY OF THE INVENTION

[0005] The present invention overcomes many of the disadvantages of theprior art by providing, in one aspect, an injection molding apparatuscomprising a first array of injection nozzles and a second array ofinjection nozzles, each nozzle having a melt channel and a valve pinmovable within the melt channel to open and close a mold gate. A meltdistribution manifold is located between the first and second arrays ofinjection nozzles and is in fluid communication with the arrays ofnozzles. Separate actuating assemblies are provided, one for displacingthe valve pins of the first array of injection nozzles and another fordisplacing the valve pins of the second array of injection nozzles. Eachactuating assembly comprises at least one actuator and a common linkageelement driven by the actuator and linked to all of the valve pins ofits res pective array of injection nozzles to move the valve pins inunison.

[0006] In another aspect the invention provides an injection moldingapparatus comprising an array of injection nozzles, and a meltdistribution manifold in fluid communication with the array of injectionnozzles. Each nozzle has a melt channel and a valve pin movable withinthe melt channel; and each valve pin has a driven portion and a tip endthat controls melt flow through a mold gate. An actuating assembly fordisplacing the valve pins of the array of injection nozzles comprises atleast one actuator and a common linkage element driven by the actuatorand linked to the driven portions of all of the valve pins of the arrayof injection nozzles to move the valve pins in unison, the actuatorbeing located between the common linkage element and the tip ends of thevalve pins.

[0007] Further objects and advantages of the invention will appear fromthe following detailed description taken together with the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWING

[0008]FIG. 1 is a partial sectional view of a portion of a multi-cavitystack molding system according to a first embodiment of the invention,showing the valve pins in the open position;

[0009]FIG. 2 is a partial sectional view of the stack molding system ofFIG. 1, showing the valve pins in the closed position;

[0010]FIG. 3 is an enlarged sectional view, taken along line 3-3 in FIG.1, of a portion of the stack molding system of FIG. 1, showing the valvepins in the open position;

[0011]FIG. 4 is view similar to FIG. 3, taken along line 4-4 in FIG. 2,showing the valve pins in the closed position;

[0012]FIG. 5 is a partial sectional view of a portion of a multi-cavitystack molding system according to a second embodiment of the invention,showing the valve pins in the open position;

[0013]FIG. 6 is a partial sectional view of the stack molding system ofFIG. 5, showing the valve pins in the closed position;

[0014]FIG. 7 is a partial sectional view of a portion of a multi-cavitystack molding system according to a third embodiment of the invention;

[0015]FIG. 8 is a partial sectional view of a portion of a multi-cavitystack molding system according to a fourth embodiment of the invention;

[0016]FIG. 9 is a partial sectional view of a portion of a multi-cavitystack molding system according to a fifth embodiment of the invention;

[0017]FIG. 10 is a partial sectional view of a portion of a multi-cavitysingle-face molding system embodying some of the features of theinvention;

[0018]FIG. 11 is a detail sectional view of guiding and attachmentelements useful in all of the above embodiments of the invention; and

[0019]FIG. 12 is a detail sectional view of an alternate form of guidingelements useful in all of the above embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Reference is first made to FIG. 1 which shows a portion of astack mold assembly 1 comprising a stationary, elongated and heated meltdistribution manifold 2 having a central melt bore 20. Backing plates 3surround manifold 2 and tightly abut one another. Above and belowbacking plates 3 are nozzle plates 4, each of which houses a pluralityof valve gate nozzles 9 (here, four nozzles in a single row) mounted inseparate nozzle bushings 21.

[0021] Referring to FIGS. 1 and 3, each valve gate nozzle 9 has a meltbore 10 a that communicates at its outer (gated) end with a mold cavity13, and at its inner end with central melt bore 20 in manifold 2 via abranch melt passage 25 in nozzle bushing 21. To keep the resin meltheated and thus insure that it flows from central melt bore 20 througheach nozzle 9 to each cavity 13, electric heaters 22, 23, 24 areprovided, respectively, in manifold 2, each nozzle bushing 21 and thebody of each nozzle 9. Each valve gate nozzle 9 has a single valve pin10 with a head 12. The front end of the pin 10, i.e., the end adjacentthe gate, controls melt flow through the gate.

[0022] Nozzle plates 4 also house actuating assemblies 6. Each actuatingassembly 6 comprises two double-acting hydraulic actuators 7 that flankthe array of valve gate nozzles 9 that they actuate, each having a cap15 at its outer end and driving a rod 16 at its inner end which extendsfrom the internal piston of the actuator. A yoke plate 8 is disposedbetween manifold 2 and each array of valve gate nozzles 9, and is linkedto rods 16 of the adjacent actuators 7. The heads 12 of valve pins 10are engaged with their adjacent yoke plates 8. Movement of each yokeplate 8 by actuators 7 thus simultaneously moves the adjacent array ofvalve pins 10 between open and closed positions. Spacers 11 fixed to theends of yoke plates 8 serve as stops for the yoke plates. Thearrangement of actuators 7 and yoke plates 8 is symmetrical so that theforces applied by the actuators are evenly distributed.

[0023]FIG. 11 shows details of the connection of yoke plates 8 to rods16, and the structure for guiding the yoke plates. Each rod 16 has aterminal portion 30 with a shoulder 32 and an internally threaded bore34. Terminal portion 30 mates with a similarly shaped hole 18 in yokeplate 8. A washer 36 and a cap bolt 38 tightly secure yoke plate 8 torod 16 so that they move as a unit.

[0024] Referring further to FIG. 11, each yoke plate 8 is guided by aplurality of guide pins 17 that are fixed to nozzle plates 4 and extendthrough holes 27 in the yoke plate. Guide pins 17 and holes 27preferably have circular cross-sections, but other cross-sections may beused as long as they allow for a close sliding fit. An anti-frictionelement in the form of a bushing 19 a lines each hole 27 such that thereis a smooth sliding fit between pins 17 and holes 27. FIG. 12 shows analternate arrangement wherein the anti-friction element is in the formof a sleeve carried on the outside of each pin 17. Either arrangementsmoothly and evenly guides the yoke plates 8 under the action ofactuators 7, preventing warping of the yoke plates 8 and insuringuniform loading of the valve pins 10.

[0025] The anti-friction elements between pins 17 and holes 27 in yokeplates 8 can be made of any thermally stable, low-friction polymer.Examples include polyamide or polytetrafluoroethylene (PTFE); or acomposite polymeric composition, for example, metalfluoroplasticmaterial; or a low-friction alloy, for example, sintered bronze. It isalso possible to use a wear-resistant solid lubricating coating, forexample, a polymeric, ceramic or hard metal coating capable of stableoperation under conditions normally encountered during the injectionmolding process, and also capable of being fused either on the outsideof pins 17 or on the inside of holes 27.

[0026] In use, a controlled external source of hydraulic fluid (notshown) connected to actuators 7 drives each linked pair of actuators inthe same direction as required during the molding operation. FIG. 1shows all of the valve gates in the open position, which allows resinmelt to flow into all mold cavities 13. When the cavities are filledwith resin, hydraulic pressure applied below the pistons of upperactuators 7 causes upper rods 16 to move upwardly and carry with themupper yoke plate 8, thus moving upper valve pins 10 upwardly in unisonto close the upper valve gates and stop melt flow. Similarly, hydraulicpressure applied above the pistons of lower actuators 7 causes lowerrods 16 to move downwardly and carry with them lower yoke plate 8, thusmoving lower valve pins 10 downwardly in unison to close the lower valvegates and stop melt flow. The closed configuration is depicted in FIG.2. After the molded articles are removed and it is desired to resumemelt flow into the cavities 13, the process is reversed to open all ofthe valve gates, returning to the configuration of FIG. 1.

[0027]FIGS. 1 and 2 demonstrate that both arrays of valve gate nozzlesare actuated simultaneously, all being either open or closed at the sametime. In other words, melt injection occurs simultaneously through allof the valve gates. If desired, each array of valve gate nozzles may beindependently controlled by a suitable hydraulic controller that wouldindependently direct pressurized hydraulic fluid as desired to the pairof actuators 7 of each array of nozzles. Thus the gates of one array ofnozzles may be held open to allow melt flow while the gates of the otherarray may be held closed to block melt flow.

[0028] A second embodiment of the invention is depicted in FIGS. 5 and6. This embodiment has a layout similar to the first embodiment (likeparts are denoted by like reference numerals), but movement of yokeplates 8 is effected by two-cylinder double-acting pneumatic actuators207, instead of hydraulic actuators. Also, each heated valve gate nozzle209 houses a plurality of valve pins 210, a central melt bore 210 a andbranch melt bores 210 b which feed separate mold cavities 213. Ofcourse, pneumatic actuators can be used in a stack mold arrangementhaving valve gate nozzles with single valve pins.

[0029]FIG. 7 depicts a third embodiment of the invention, in which likeparts are denoted by like reference numerals. Here, a more elongatedheated melt distribution manifold 302 has a plurality of central meltbores 320 that communicate with plural-pin heated valve gate nozzles309, each of which feeds a single local mold cavity 313. Movement ofeach yoke plate 8 is effected by a single centrally located,two-cylinder, double-acting pneumatic actuator 307. Of course, centrallylocated pneumatic actuators can be used in a stack mold arrangementhaving valve gate nozzles with single valve pins.

[0030]FIG. 8 depicts a fourth embodiment of the invention which isidentical to the embodiment of FIG. 7 (like parts are denoted by likereference numerals), except that conventional reversing electric motoractuators M effect movement of yoke plates 8.

[0031]FIG. 9 depicts a fifth embodiment of the invention that is similarto the embodiment of FIG. 7 (like parts are denoted by like referencenumerals). However, movement of the upper yoke plate 8 a is effected bya two-cylinder, double-acting pneumatic actuator 507, while movement oflower yoke plate 8 b is effected by a reversing electric motor actuatorM. Also, two separate heated melt distribution manifolds 502 are used.Further, melt feed to various mold cavity configurations is illustrated.Specifically, the right side of FIG. 9 shows an arrangement wherein thefour branch melt bores of two heated valve gate nozzles feed a singlelarge mold cavity 513 a; to the left of that the two branch melt boresof a single heated valve gate nozzle feed a single smaller mold cavity513 b; and to the left of that the individual branch melt bores of asingle heated valve gate nozzle feed individual smaller mold cavities513 c.

[0032]FIG. 10 illustrates how some of the features of the invention canbe incorporated in a multi-cavity single-face molding system (like partsare denoted by like reference numerals). This embodiment essentially isthe lower half of the embodiment of FIG. 9, i.e., the upper yoke plate 8a of FIG. 9 and all structure above it has been eliminated. A singletwo-cylinder, double-acting pneumatic actuator 607 is shown, but areversing electric motor actuator (as per FIG. 9) may be used instead.

[0033] From the above it will be appreciated that the invention affordsflexibility in construction and operation of a molding apparatus that isdurable and relatively compact, and operates efficiently and reliably.While the features of the invention have been described in the contextof one or more preferred embodiments, it will be evident that variousmodifications are possible without departing from the scope of theinvention as understood by those skilled in the art and as defined by inthe following claims.

1-40 (Cancelled).
 41. A stack injection molding apparatus comprising: aninjection manifold having a melt inlet, a plurality of first meltoutlets and a plurality of second melt outlets; a first plurality of hotrunner nozzles in communication with said first plurality of meltoutlets facing a first plurality of mold cavities, wherein said firstplurality of mold cavities are located on a first mold plate; a secondplurality of hot runner nozzles in communication with said secondplurality of melt outlets facing a second plurality of mold cavities,wherein said second plurality of mold cavities are located on a second,movable mold plate; a first actuation means connected to a firstplurality of valve pins movable at least in a single nozzle of saidfirst plurality of hot runner nozzles; and a second actuation meansconnected to a second plurality of valve pins movable at least in asingle nozzle of said second plurality of hot runner nozzles, whereinthe injection manifold is located between said first and said secondactuation means.
 42. A stack injection molding apparatus according toclaim 41, wherein said first and second actuation means are pistons. 43.A stack injection molding apparatus according to claim 41, wherein saidfirst and second actuation means independently move said first and saidsecond plurality of valve pins.